The present invention relates to cutting tools used for mining and excavation purposes. The present invention has been developed principally for use in the mining of coal and in that use, typically underground coal mining. It will therefore be convenient to describe the invention in relation to that use although it will be readily appreciated that the invention could be employed for any mining or excavation operation to which its function is suitable.
Various different forms of equipment and machinery can be employed for mining and excavation operations, and typically it is the type of mining or excavation taking place, and the type of earth being mined or excavated, that dictates the type of equipment and machinery that is appropriate. The present invention is principally concerned with underground coal mining and one of the major safety difficulties is that type of mining relates to fires or explosions within the mine. These can occur due to the generation during mining of methane gas and coal dust (commonly known as mine dust), which can be trapped within the mine and is readily ignitable. Disadvantageously, the equipment used in coal mining can generate incendive sparks and thus cause fires or explosion. As used herein, incendive means capable of causing fire, i.e. incendiary. Therefore, it is important that all appropriate steps be taken to minimize or eliminate the production of sparks.
Equipment used to mine or excavate in hard earth can include rotary cutters, in which a rotating drum that carries a plurality of projecting cutting bits or picks, is brought into engagement with an earth face. The picks bite into the earth face as they rotate with the drum, to impact against and to dislodge or fragment earth from the face. This highly aggressive engagement between the picks and the earth face can result in spark production between them.
Picks employed for the above purpose generally have a hard cemented tungsten carbide tip that is fixed, usually by brazing, to a steel shank. Picks of this kind are disclosed in various prior art, such as U.S. Pat. No. 6,113,195, EP-0274645 and DE-4226976. The tip of the picks can be either of the insert or cap style.
The insert style is shown in DE-4226976, in which a greater section of the axial length of the tip is anchored within a bore of the shank, than extends out of the bore. The cap style is shown in EP-0274645, in which the tip has a broader base than the insert style tip and the base is located and brazed into a relatively shallow recess in the forward end of the shank. The present invention is applicable to either of these forms of pick.
In picks of the above kind, sparks can be produced between the tungsten carbide tip and the earth face and also between the steel shank and the earth face, although there typically is greater likelihood of spark production between the shank and the earth face.
It is an object of the present invention to provide a cutting pick which has a reduced likelihood of producing a spark during mining or excavation operations, in particular underground coal mining.